//回文串的个数

class Solution {
public:
    int countSubstrings(string s) {
        int n = s.size();
        vector<vector<bool>> dp(n, vector<bool>(n));
        int ret = 0;
        for(int i = n - 1;i >=0; i--)
        {
            for(int j = i; j < n; j++)
            {
                if(s[i] == s[j])
                {
                    dp[i][j] = i + 1 < j ? dp[i + 1][j - 1] : true;
                    if(dp[i][j]) ret++;
                }
            }
        } 
        return ret;
    }
};